1. Field of Invention
This invention relates to a method and apparatus for automatically punching or pressing products out of sheet material positioned by using a visual sensor.
2. Description of the Prior Art
When working material with a press machine, it is usual to supply the sheet of material to the press machine such that the working reference center of the material would coincide with the working position of the press, for example a die center. Especially, when punching a plurality of printed patterns from a sheet of material or a work piece with the press machine, it is necessary to accurately position the material with reference to the press machine.
According to a prior art method of press punching, at a first step (I), a sheet of material 1 on which a plurality of printed portions 1a and a plurality of marks M utilized to position the sheet at the time of punching the printing portions 1a are printed is divided in to a plurality of sections which a shear as shown in FIG. 1, at a second step (II), guide openings M' are formed through each divided section with a table type drill according to the marks M, and at step (III) guide pins 2a of the metal mold 2 of the press machine are inserted into the guide openings for positioning printed portions 1a, thus punching products 3.
With such prior art method, however, it is difficult to continuously feed the sheet of material to the press machine. Moreover, as it is necessary to form guide openings through the sheet of material, there is a defect that the working efficiency is low.
To solve these problems, an improved method of supplying the material has been proposed as disclosed in U.S. patent application Ser. No. 535,677 and West Germany Patent Application No. 33351643 in which the material is positioned by using a visual sensor.
This improved method of feeding a sheet of material will be described with reference to FIG. 2. More particularly, a sheet of material 1 is moved in the X and Y directions of rectangular coordinates by a material feed device 20, thus feeding the sheet of material 1 to a press machine 10 provided with a camera 11. The material feed device 20 will be described in more detail with reference to FIG. 3.
In this device, a beam 22 is mounted on rails 21a and 21b on the opposite sides of the device and moved along the rails in the Y direction by rotating a ball screw 23. A clamper carrier 24 is suspended from the beam 22, which is moved along the beam in the X direction. The clamper carrier 24 is provided with clampers, not shown, for clamping therebetween the sheet of material 1. With this material feed device the sheet of material 1 can be moved in X and Y directions along a supporting table 25. In order to move smoothly the sheet of material 1 on the supporting table 25, supporting balls B1-B25 are embedded in the supporting table 25.
As shown in FIG. 4, each supporting ball B is biased upwardly by a spring S and can rotate in any direction. The ball is pushed down when a force larger than a predetermined value is applied thereto. Normally, the ball B projects from the surface of the supporting table by a height h which coincides with the material clamping surface of the pawls 26b of the clamper 26. The clamping pawls 26b are caused to clamp or release the sheet 1 by driving the pawls 26b in the direction A or B by a pneumatic cylinder 26c.
Consequently, when the ball B is completely projected upwardly, the sheet of material 1 can slide on the ball and the work clamper 26 pass over the ball B while depressing the ball B by an.amount equal to the plate thickness of the pawls 26b. This construction enables to move flat sheet of material on the supporting plate 25 without dropping or damaging the material.
As shown in FIG. 5, the supporting table 25 is provided with a suction transport mechanism located beneath the table 25 and a stop member 28 at the righthand end thereof so that the clampers 26 can automatically and accurately clamp the sheet of material 1 at a correct attitude.
The suction transfer mechanism 27 includes movable tables 271 and 272. The lower ends of the opposite ends of the table 27 are fit on guide grooves 274 and 275 provided in the X direction for a box shaped base frame 273, whereas the lower projections 278 and 279 of the table 272 are received in guide prooves 276 and 277 formed in the Y direction for the table 272.
The base frame 273 is provided with a pneumatic cylinder 280 extending in the X direction, while a pneumatic cylinder 28 is mounted on the table 271 to extend in the Y direction. The piston rod of the pneumatic cylinder 280 is connected to table 271, while the piston rod the pneumatic cylinder 281 is connected to the table 272.
Horizontally spaced apart pneumatic cylinders 282 and 283 are secured vertically on the table 272 and vacuum cups 284 and 285 are attached on the upper ends of their piston rods.
Since the suction transfer mechanism 27 has a construction as above described, by operating cylinders 280 and 281 the vacuum 284 and 285 can be moved simultaneously in X and Y directions by distances corresponding to the strokes of the pistons of the pneumatic cylinders. Moreover, by actuating pneumatic cylinders 282 and 283, the vacuum cups 284 and 285 are raised or lowered.
Turning back to FIG. 2, rectangular windows 29a and 29b are provided for the table 25 for permitting vacuum cups 284 and 285 to project above the table and for moving these cups in the X and Y directions.
The operation of the suction transfer mechanism 27 will now be described. Suppose now that the sheet of material 1 has been brought on the table 25 as shown in FIG. 6a by a suitable transfer device, not shown. Then the vacuum cups 284 and 285 will project beyond the surface of the table 25 to suck the lower surface of the sheet 1. Then, the cylinder 281 is actuated to move the vacuum cups in the Y direction together with the sheet 1 until its righthand edge comes to abut the stop member 28, whereby the attitudes of the sheet 1 is corrected. Then the vacuum cups 284 and 285 are moved in X direction by the pneumatic cylinder 50 so that the front edge of the sheet 1 engages the base portions of the clamping pawls 26a to correctly position the sheet 1 as shown in FIG. 6c. In this manner, the suction transfer mechanism 27 and the stop member 28 act as a positioning means of the sheet.
The sheet 1 thus positioned is clamped by clamping pawls 26a and 26b and then moved in X and Y directions by the clamp carrier 24.
To correctly position the sheet 1, at first, the position of the sheet 1 is coarsely adjusted such that its mark M would lie in the field of view of camera 11, as shown in FIG. 7. Then sheet 1 is moved in X direction from a position Xs to XE (which is called subscanning) and at the same time the sheet is scanned by a visual sensor in Y direction in a predetermined field of view, this scanning being called a main scanning.
The deviation x, in the direction of X between the center Xc of the sub-scanning and the center C of the mark M is detected by the difference the mean value of a sub-scanning position Xa at which the mark X is detected first and a sub-scanning position Xb at which the mark M is detected at the last, and the center position Xc of the sub-scanning. The deviation y in Y direction between the center position Ys of the main scanning and the center position C of the reference mark M is detected by the mean value of the difference between distance la between the upper limit of the field of view at the time of main scanning and the reference mark M, and the distance lc between the periphery of the reference mark M and the lower limit of the field of view.
Since the positional relation between the punching center W of the press machine 10 and the camera 11 is preset, at the time of supplying the sheet to the punching center W, the preset amount of movement is corrected by the detected deviation .DELTA.X in the X direction and the deviation .DELTA.Y in the Y direction so as to supply the sheet with the corrected amount of movement.
The method of detecting the deviations .DELTA.X and .DELTA.Y and the method of supplying the sheet will be described in detail with reference to FIGS. 8 through 12.
FIG. 8 shows a block diagram of the control system of the automatic punching apparatus shown in FIG. 2 in which a sensor control unit 40 is used for outputting a scanning instruction signal S1 to the camera 11 and for processing an image signal S2 picked up by the camera 11 in a manner to be described later. The output of the sensor control unit 40 is fed to a central processing unit (CPU) through a sensor interface and a bus line 42. A X unit drive unit 44 is used for driving the clamper carrier 24 shown in FIG. 2 and is constituted by a drive shaft 44a threaded into a threaded member 24a provided for the clamper carrier 24 for moving the same, an electric motor 44b for driving the drive shaft 44a, a pulse encoder 44c coupled to the drive shaft 44a for generating two pulse signals P1 and P2 having the same waveform but having different phases, a speed detector 44d driven by the motor 44b for generating a signal proportional to the rotational speed of the motor, and a servo-amplifier 44e supplying a drive signal to the drive motor 44b.
A Y axis drive unit 45 is provided for driving the beam 22 and table 25 shown in FIG. 2 and is constituted by an electric motor 45a for driving a drive pulley 23a, a pulse encoder 45b coupled to the motor 45a for generating two pulse signals P3 and P4 having the same wormform but having different phases, a speed detector 45c detecting the rotational speed of the motor 45a and a servoamplifier 45d supplying a drive signal to the motor 45a.
The speed detector 44d, and servoamplifier 44e; speed, detector 45c and servoamplifier 45d respectively constitute a speed feedback loops.
Pulse outputted by the pulse encoders 44c and 45h are applied to forward and reverse rotation judging circuit 46 and 47 respectively. These judging circuits 46 and 47 judge whether motors 44 and 45 rotate forwardly or reversely in accordance with the phase relation between pulse signals P1 and P2 and that between pulse signals P3 and P4. When it is judged that the motors are rotating in the forward direction, the judging circuits output signals S3 and S4 of a logic level H. Furthermore the judging circuits output movement pulse signals P5 and P6 respectively showing that X and Y axes have moved one step each time a predetermined number of pulse signals P1 (or P2) and pulse signals P3 (or P4) are inputted. Signal S3 and pulse signal P5 are applied to the control input terminal U/D and clock input terminal of a up down counter 48, and to a sensor control unit 40, while signal S4 and pulse signal P6 are applied to the control input terminal U/D and clock input terminal CK of a up down counter 49.
The outputs of up down counters 48 and 49 are applied to CPU 43 via bus line 42 to act as X axis position data and Y axis position data respectively. Based on the X axis position data and the Y axis position data, CPU 43 calculates position deviation data for each shaft and supplies the calculated data to the servoamplifiers 44 and 45 respectively via bus line 42, D/A converters 50 and 51 and preamplifiers 52 and 53.
The press machine 10 works a single sheet of material 1 to form a plurality of products. As shown in FIG. 1, the sheet is formed with circular marks M near portions of the sheet 1, to be punched, the marks having reflective index different from that of the sheet 1. The positions of these marks are prestored in a memory device 54 as X and Y rectangular coordinate data of the material supply device 22 representing the position of the sheet 1 when it is clamped by the clamper 26 at a predetermined portion. Due to the sitting error of the sheet 1 or misalignment of prints, the coordinate data do not accurately represent the center positions of the marks. For this reason, it is necessary to correct the positions as will be described later.
At first, the CPU 43 roughly determines the position of the sheet of material 1 based on the coordinate data. At this time, the line image sensor photographs the position Xs on the sheet of material 1 shown in FIG. 7 for a line length V. The CPU 43 operates the sensor control unit 40 and the X axis drive mechanism 44 to measure the center position of the mark M.
As shown in FIG. 9, the sensor interface 41 comprises a flip-flop circuit 41a and bus buffer memory devices 41b, 41c and 41d. The output terminal Q of the flip-flop circuit 41a is connected to one input of an AND gate circuit 40a comprising the sensor control unit 40, while the output terminals Q of counters 40b, 40c and 40d are connected to the input terminals A of the bus buffer memory devices 41b 41c and 41d respectively.
The output signal S3 of the forward and reverse rotation judging circuit 46 and the pulse signals are supplied to respective inputs of an AND gate circuit 40e, the output terminal thereof being connected to the other input terminal of the AND gate circuit 40a. The output signal of the AND gate circuit 40a is supplied to the scanning control unit 11a of the camera 11 to act as the scanning control signal S1. Further, the output of the AND gate circuit 40a is converted into a signal S5 by a delay waveform shaping circuit 40 and then supplied to the latch instruction input terminal L of the register 55 and to the CPU 43.
When supplied with signal S1, the scanning control unit 11a applies a scanning pulse P7 to the line image sensor 11b for sequentially scanning light receiving cells thereof. Further, the scanning control unit 11a judges that whether an image signal S6 outputted from the line image sensor 11b represents a bright portion or not. When the image signal represents the bright portion, the scanning control unit 11a produces a bright portion signal S2a, but if not produces a dark portion signal S26. The scanning control unit 11a produces a start signal S7 and an one scanning termination signal S8 respectively at the times of starting and terminating the scanning, and a clock signal P8 synchronous with the scanning of the line image sensor 11b. Where the reflection index of the mark M is smaller than that of the sheet 1, the scanning control unit 11a produces a signal S9 of logic level H. The optical system 11c focusing a picture image on the light image sensor 11b is constituted by a combination of lenses.
Signal S2a is applied to the input terminal A of a selector 40g and to the input terminal B of a selector 40h. Signal S2b is applied to input terminals B and A of the selectors 40g and 40h respectively, while signal S9 is supplied to the control input terminals S of the selectors 40g and 40h respectively. Signal S7 is applied to reset terminals R of counters 40b, 40c and 40d and flip-flop circuit 40i. Signal S8 is supplied to the CPU 43 via an inverter 40j, while the clock signal P8 is applied to one inputs of AND gate circuits 40k, 40l and 40m. The output signal S10 of the selector 40g is applied to the set terminal S of the flip-flop circuit 40i and to the other input terminal of the AND gate circuit 40k, while the output signal S11 of the selector 40h is applied to the other input terminals of AND gate circuits 40 l and 40m. The output signal S12 of the flip-flop circuit 40i is applied to the other input terminal of the AND gate circuit 40m and to the other input terminal of the AND gate circuit 40l.
When the reflective index of the mark M is smaller than that of the sheet 1 (that is when the mark M is made of black and lusterless paint or the like) and when the line image sensor 11b is scanning a X coordinate Xi including mark M, the scanning control unit 11a changes the logic level of the signal Se to L whereby selectors 40g and 40h output signals applied to their input terminals B from their output terminals.
The flip-flop circuit 41a has already been set by CPU 43 so that the time of positioning the sheet, the flip-flop circuit 41a outputs a signal S1 to the scanning control unit 11a corresponding to signal P5 outputted from the forward reverse judging circuit 46.
As a consequence, the scanning control unit 11a produces a start pulse S7 as shown in FIG. 10a to reset the flip-flop circuit 40i, counters 40b, 40c and 40d and then outputs a scanning pulse P7 to the line image sensor 11b to cause it to scan from point PA, and a clock signal P8 (FIG. 10b) synchronous with the scanning pulse P7.
The line image sensor 11b generates a signal S6 which represents a bright portion while scanning between points PA to PB and between point PC and end point, and represents a dark portion while scanning between points PB and PC. Consequently, the scanning control unit 11a produces a signal S2a which becomes H level during the scanning between points PB and PC and signal S26 which becomes H level during the scanning between points PA and PB and between point PC and the end points.
Thus, the output signals S10, S11 and S12 of the selectors 40g and 40h and flip-flop circuit 40i become as shown in FIGS. 10d, 10e and 10f respectively with the result that the clock signals outputted by AND gate circuits 40k, 40l and 40m change as shown in FIGS. 10g, FIG. 10h and FIG. 10i respectively.
Accordingly, the counts of counters 40b, 40c and 40d respectively represent the distance lb between points PB and PC (the length of mark M along coordinate X1), the distance la between points PA and PB (the distance between the scanning starting point along the coordinate X1 and the upper most portion of mark M) and the distance lc between point PC and the scanning end point (the distance along coordinate X1 between the lowermost portion of mark M and the scanning end point).
Signal S8 (see FIG. 10c) outputted from the scanning control unit 11a at the time of terminating the scanning is inverted by inverter 40j to produce a signal 8 which is applied to CPU 43 as a first interruption signal.
The signal S5 outputted by the delay waveform shaping circuit 40f builds up at a point later by than the build down point of signal S1 to become H level for a predetermined time. This signal stores the count (representing X1 which is the X coordinate at this time) in the register 55. The signal S5 acts as a second interruption signal for CPU 43 so that the CPU 43 takes the data stored in the register 54 into its input 60 to store the data in the memory device 54 (step 61). Then the program is returned to the original state.
Where the reflective index of the mark M is higher than that of the sheet 1, the logic level of the signal S9 becomes H. Thereafter, processings similar to those described above are executed.
Each time the first interruption signal S8 is applied, CPU 43 executes a control as shown in FIG. 12 to detect the position of the center position of mark M.
More particularly, at step 70, the content of the counter 40b, that is the distance lb is inputted for storing the same in a predetermined region of the memory device 54 at step 71.
In an area between the subscanning starting position Xs and the coordinate position Xa, since the mark M does not present, the distance lb is zero. As a consequence, the result of judgment at step 72 as to whether the distance lb is zero or not becomes YES. Then, at step 73, the content of the counter 40b, that is distance lb which has been stored at the time of previous interruption is read out. Since l'b is also zero, the result of judgment at step 74 as to whether the distance l'b is zero or not becomes NO. Accordingly, the CPU 43 returns to the processing of the main routine which CPU 43 has been processed before occurrence of an interruption.
At the coordinate Xa corresponding to an edge of mark M, since distance lb is not zero, the result of judgment at step 72 is NO. Moreover, since distance l'b read out at step 72 is identical to step 73 is also zero, the result of judgment at step 76 as to whether distance l'b is zero or not becomes YES. At step 77, CPU 43 stoes the data stored at step 61, that is the data stored in the register 55 in the memory device 54 as the coordinate Xa. At step 78, a zero is substituted for variables Ns and .DELTA.Y so as to reset these variables. Thereafter the program returns to the processing of the main routine.
In a region in which the mark M presents, since both lb and l'b are not zero, the results of judgments executed at steps 72 and 76 are both NO. Accordingly, the counts of counters 50a and 40d, that is the data regarding distances la and lc are applied to CPU 43 at step 79 so that the value of .DELTA.Y is updated according to the following equation and the value of the variable Ns is incremented by 1. ##EQU1##
Thereafter the program returns to the main routine.
At a coordinate Xb representing an edge of mark M opposite to that represented by coordinate Xa, since distance lb is zero and since distance l'b is not zoro, the result of judgment executed at step 72 becomes YES and the result of judgment executed at step 74 also becomes YES. Accordingly, at step 81, the data stored in the register 55 at step 61 is read out and stored in the memory device 54 as a coordinate Xb. Then at step 82 deviations .DELTA.Xc and .DELTA.Yc of the X and Y coordinates of the center position of mark M are calculated according to the following equations (2) and (3) and these calculated deviations .DELTA.Xc and .DELTA.Yc are stored at step 82. ##EQU2##
Thereafter the program returns to the main routine.
The area between the coordinate Xb and coordinate Xe, that is the end point of sub-scanning is processed in the same manner as the area between coordinates Xs and Xa.
The CPU 43 corrects the data prestored in the memory device 54 based on the deviations .DELTA.Xc and .DELTA.Yc thus calculated, and then determins the position based on the corrected position coordinates, thus enabling to correctly set the printed position at the punching center W of the press machine 10.
Where printed portions formed on the sheet 1 in a plurality of rows as shown in FIG. 13 are to be punched with press machine 10, the CPU 43 controls the press machine 10 and the material supply device 20 in the following manner.
More particularly, regarding the first row marks M, the CPU 43 sequentially detects deviations .DELTA.Xc and .DELTA.Yc of the X and Y coordinates of the actual center position with respect to the prestored reference position, starting from the left end mark M (see FIG. 13b). At this time, the CPU 43 holds the press machine 10 at its upper dead center.
Then by using the deviations .DELTA.Xc and .DELTA.Yc, the CPU 43 sequentially positions the printed portions 1a at the punching center W of the press machine starting from the rightmost printed portion 1a of the first row and causes the press machine to sequentially punch (see FIG. 13b). When positioning the printed portions 1a the coordinates of the reference positon of each printed portion 1a are corrected by the deviations .DELTA.Xc and .DELTA.Yc.
Then CPU 43 moves the sheet 1 in a direction shown by an arrow in FIG. 13c so as to position the left end mark M of the second row at a positon just below camera 11 (see FIG. 13d) so as to control the printed portions 1a of the second row for punching them with the press machine 10.
In the same manner, the CPU 43 causes the press machine 10 to sequentially punch printed portions 1a of the third and following rows.
In accordance with the crank angle rotation data applied from the press machine 10 via input interface 56 and bus line 42, the CPU 43 controls the positioning of the sheet 1 in synchronism with the operation of the press machine 10. Also the CPU 43 supplies a upper dead center stop instruction to the press machine 10 via bus line 52 and output interface 57 to stop the crankshaft of the press machine 10 at the upper dead center.
Generally, before press work, the printed sheet 1 (see FIG. 1) is inspected by eyes of the operator and printed portions 1a of deficient printing or having defects are marked with X. For the purpose of not punching such defective printed portions 1a, a method has been proposed in which before starting the punching operation, the position data regarding defective printed portions 1a are stored by using an operating pawl or the like so that positioning would not be made at memory areas storing defective printed portions.
This method, however, requires much time for inputting position data of defective printed portions. Moreover, inputting of the position data is not only troublesome but also accompanies input errors.
In a system wherein positioning is made by using a visual sensor, when it does not operate normally, it is difficult to accurately determine the center position of the mark, thus causing erroneous punching.
Moreover, for positioning the sheet 1 to the clamper 26, vacuum cups 284 and 285 are moved in two directions of X and Y so that it is necessary to use independent cylinders 280 and 281 for the two directions. As a consequence, the construction of apparatus comprising electromagnetic valves and electric circuits that control the cylinders becomes complicated and expensive.
Since a force is not applied to the sheet in the Y direction while the vacuum cups 284 and 285 are being moved in X direction, position of the sheet 1 will be shifted more or less to the left as viewed in FIG. 6c. In addition, there are the following problems. More particularly the sheet lis generally applied with a vinyl cover for protecting the printed surface and in many cases the edges of the cover project beyond the edges of the printed surface. For this reason, with prior art means for positioning sheet 1 with respect to clamper 26, the projected cover portion would be clamped between the right side edge of the sheet 1 and stop member 28 with the result that the sheet 1 would be displaced to the left by the cover at a stage for assuming the state shown in FIG. 6c.
Where the clamper 26 clamps the sheet 1 in an inclined state as shown in FIG. 14 or where not aligned printings are made on the sheet 1 as shown in FIG. 15, even when the center position of the mark is accurately determined with a visual sensor, correct punching could not be made.
More particularly, when the center position of the marks at both ends of the sheet 1 are caused to shift by .DELTA.y in Y direction as shown in FIG. 16 due to not aligned printings, the printed portion 1a to be punched would shift from a position shown by dot and dash lines to a solid line position as shown in FIG. 17. Let us denote the distance between marks M at the opposite ends by l, the distance between a mark M and the center of a printed portion 1a by X, punching error in X direction by .DELTA.x, and the punching error in Y direction by .DELTA.y. Then from the relation between FIGS. 10 and 17 the following equation holds EQU l:.DELTA.y=x:.DELTA.x (4)
By modifying this equation with reference to .DELTA.x, we obtain ##EQU3## Putting l=1000 mm, x=25 mm and .DELTA.y=1 mm, from equation (5) we can obtain X=25 microns. In other words, even when the center position of the mark is accurately detected, at a position spaced 25 mm from the center of the mark, a punching error of 25 microns in the X direction is inevitable.
The camera 11 utilized in the automatic punching system has a resolution of 0.025 mm and since the depth of view photographed without blurring the picture image is only .+-.0.6 mm, when the thickness of the sheet 1 varies by more than .+-.0.6 mm, it is impossible to obtain accurate picture images, thus failing accurate positioning.
To obviate this problem, apparatus has been proposed wherein the camera is moved in the vertical direction in accordance with the thickness of the sheet so as to automatically focus the camera.
Although this apparatus can automatically focus, it is necessary to use a motor for vertically moving the camera, position detector, etc., thus increasing the size and cost. Where the thickness of the sheet does not vary appreciably, it is advantageous to manually adjust the camera.
Where supporting balls B1-B25 are arrayed as shown in FIG. 3, there is the following difficulty when the center position of the positioning mark is detected by the camera.
Thus, as shown in FIG. 18, when an end of the sheet 1 is brought between supporting balls B2 and B3, since the sheet 1 is thin it droops owing to the weight thereof so that the surface position of the sheet 1 displaces by .DELTA.l with reference to the optical axis of the camera with the result that the focal point of the camera is displaced, thus blurring the picture image. Especially, in a material supply apparatus with visual sensing performance, since the center position of the position determining mark is detected at a resolution of 25 .mu.m/bit, it is necessary to photograph from a position of short distance. As a consequence, the focal depth is very shallow of the order of .+-.1 mm, whereby it is greatly influenced by the drooping of the sheet 1.